1. Field of the Invention
The field of the endeavor of the invention relates to ground planes for antennas and in particular to a method of reducing surface currents induced by the antenna on the ground plane.
2. Description of the Prior Art
A ground plane is a common feature of most radio frequency and microwave antennas. It is comprised of a conductive surface lying below the antenna and often performs a useful function by directing most of the radiation into one hemisphere in which the antenna is located. Frequently, the ground plane is present by necessity rather than by intent as in the case of a metal-skinned aircraft. For many types of antennas, the ground plane degrades antenna performance and/or dictates the antenna design itself. The most obvious constraint is that the tangent electric field on the conductive surface must be zero, so that electromagnetic waves experience a 180.degree. phase shift on reflection. This often imposes a minimum height of about a quarter wavelength on the antenna. Furthermore, RF surface currents can propagate freely along the metal surface of the ground plane. These surface currents result in lost power due to radiation from edges or other discontinuities, and interference between nearby antennas on the aircraft. In phased arrays, surface currents are particularly problematic, contributing to coupling between antenna elements and causing blind angles.
What is needed is some type of method or design which provides a metallic surface which forbids RF current propagation and reflects electromagnetic waves with zero phase shift.
What is further needed is some type of method or apparatus whereby surface currents on ground planes associated with antennas can be suppressed to provide more efficient antennas, reduce coupling between elements in a phased array, and reduce interference between nearby antennas on aircraft.
Further, what is needed is a reflector which lacks edge currents that radiate power into the back hemisphere of the antenna.
What is needed is also ground plane in which a non-shifted phase of the reflected waves enable smaller antennas to be realized, since the radiating elements can be located very near the surface of the ground plane without being shorted out by it.